The present application claims priority to Japanese Application No. P11-067031 filed Mar. 12, 1999 which application is incorporated herein by reference to the extent permitted by law.
The present invention relates to a solid electrolyte battery incorporating a wound electrode constituted such that elongated positive and negative electrodes are laminated such that a solid electrolyte is sandwiched is wound in their lengthwise direction.
In recent years, a multiplicity of portable electronic apparatuses, such as camcoders, portable telephones and portable computers, are coming. An attempt has been made to reduce the size and weight of the apparatus. Also reduction in the size and weight of a battery serving as the portable power source of the electronic apparatus is required. Therefore, a lithium ion battery capable of meeting the requirement has been developed and industrially put into practical use. The foregoing battery incorporates a porous polymer separator disposed between the positive electrode and the negative electrode and impregnated with electrolytic solution. To prevent leakage of the electrolytic solution, the overall body of the battery is packaged in a thick and heavy metal container.
On the other hand, a solid-electrolyte battery incorporating a solid electrolyte which serves as the ion conductive material acting between the positive electrode and the negative electrode is free of leakage of solution. Therefore, the solid electrolyte battery is considered to be capable of reducing the size and weight of the battery by simplifying the package. In particular, attention is focused on a solid polymer electrolyte containing lithium salt which is dissolved in polymers as solid solution and a solid electrolyte in the form of gel (hereinafter called a xe2x80x9cgel electrolytexe2x80x9d) such that matrix polymers contain electrolytes.
A gel electrolyte battery 10 incorporating the gel electrolyte, for example, as shown in FIG. 1, has a wound electrode hermetically enclosed in a casing film 11. The wound electrode incorporates an elongated positive electrode 12, an elongated negative electrode 13 disposed opposite to the negative electrode 13 and a gel electrolyte layer 14 disposed between the positive electrode 12 and the negative electrode 13. The positive electrode 12 and the negative electrode 13 are laminated such that the gel electrolyte layer 14 is sandwiched between the positive electrode 12 and the negative electrode 13. The formed laminate is wound many times in the lengthwise direction so that the wound electrode is constituted. A positive-electrode lead (not shown) is connected to the positive electrode 12, while a negative-electrode lead 15 is connected to the negative electrode 13.
The gel electrolyte battery 10 can be manufactured as follows.
The positive electrode 12 is manufactured as follows: a positive electrode mix containing a positive-electrode active material and a binder is uniformly applied to the two sides of a collector of the positive electrode. Then, the positive-electrode mix is dried so that a positive-electrode active material layer is formed. Then, drying is performed, and then a pressing process using a roll press is performed to obtain a positive-electrode sheet.
The negative electrode 13 is manufactured as follows: a negative electrode mix containing a negative-electrode active material and a binder is uniformly applied to the two sides of a collector of the negative electrode. Then, the negative-electrode mix is dried so that a negative-electrode active material layer is formed. Then, drying is performed, and then a pressing process using a roll press is performed to obtain a negative-electrode sheet.
The gel electrolyte layer 14 is formed as follows: sol electrolytic solution containing nonaqueous solvent, an electrolyte and matrix polymers is uniformly applied to the two sides of each of the positive-electrode sheet and the negative-electrode sheet, and then the two sheets are dried to remove the solvent. Thus, the gel electrolyte layer 14 is formed on the positive-electrode active material layer and the negative-electrode active material layer.
Then, the positive-electrode sheet having the gel electrolyte layer 14 formed thereon is cut into, for example, an elongated shape. Then, the gel electrolyte layer 14 and the positive-electrode active material layer in the portion in which the positive-electrode lead is welded is removed by cutting. The positive-electrode lead is welded to the cut portion so that the elongated positive electrode 12 having the gel electrolyte layer is obtained.
The negative-electrode sheet having the gel electrolyte layer formed thereon is cut into, for example, an elongated sheet. Then, the gel electrolyte layer and the negative-electrode active material layer in the portion in which the negative-electrode lead is welded is removed by cutting. The negative-electrode lead 15 is welded to the cut portion so that the elongated negative electrode 13 having the gel electrolyte layer is obtained.
Finally, the positive electrode 12 having the gel electrolyte layer 14 formed thereon and the negative electrode 13 having the gel electrolyte layer are laminated. The formed laminate is wound many times in the lengthwise direction so that the wound electrode is obtained. The wound electrode is sandwiched between the casing films 11, and then the outermost peripheries of the casing films 11 are welded to each other with heat to seal the opened portions. Thus, the wound electrode is hermetically enclosed in the casing films 11 so that the gel electrolyte battery 10 is manufactured.
The gel electrolyte battery 10 incorporating the thus-manufactured wound electrode suffers from a problem of defective sealing when the wound electrode is hermetically enclosed in the casing films 11.
The electrode leads disposed to overlap the elongated positive electrode 12 and the elongated negative electrode 13 in the widthwise direction of the electrodes 12 and 13 are welded for the overall width of the electrodes in order to reduce the internal resistance of the battery and improve the heavy load resistance.
The operation for sealing the opened portion of the casing films 11 is performed such that the space between the wound electrode and the casing films 11 is minimized to raise the volume energy density. At this time, an end of the electrode lead is sometimes caught by the sealed portion of the casing films 11, as indicated with a circle B shown in FIG. 1. FIG. 1 shows a state in which an end of the negative-electrode lead 15 has been caught by the sealed portion of the casing films 11.
If the end of the electrode lead is caught by the sealed portion of the casing films 11, the portion cannot satisfactorily be sealed. The defective sealing and a damaged portion of the casing film caused when the electrode lead has been caught result in introduction of moisture into the space between the casing films 11. Thus, an adverse influence is exerted on the performance of the gel electrolyte battery 10.
In view of the foregoing, an object of the present invention is to provide a solid-electrolyte battery which is capable of preventing a problem that an electrode lead is caught by casing films when the casing films are sealed without any deterioration in the heavy load resistance and preventing defective sealing.
To achieve the foregoing object, according to one aspect of the present invention, there is provided a solid-electrolyte battery comprising: an elongated electrode; a positive-electrode lead connected to the positive electrode such that the long side of the positive-electrode lead is substantially in parallel with the widthwise direct ion of the positive electrode and formed into substantially a rectangular shape; an elongated negative electrode disposed opposite to the positive electrode; a negative-electrode lead connected to the negative electrode such that the long side of the negative-electrode lead is substantially in parallel with the widthwise direction of the negative electrode and formed into substantially a rectangular shape; and a solid electrolyte layer formed on at least either surface of the positive electrode and the negative electrode, wherein the positive electrode and the negative electrode are laminated such that the surfaces on each of which the solid electrolyte layer is formed are disposed opposite to each other and wound in the lengthwise direction so as to be accommodated in a case of the solid-electrolyte battery, and a short side of at least either of the positive-electrode lead or the negative-electrode lead which is connected to the positive electrode or the negative electrode such that the short side is disposed opposite to the lengthwise end of the positive electrode or the negative electrode is shifted inwards as compared with the lengthwise end of the positive electrode or the negative electrode.
The solid-electrolyte battery according to the present invention has the structure that the short side of at least either of the positive-electrode lead or the negative-electrode lead which is connected to the positive electrode or the negative electrode such that the short side is disposed opposite to the lengthwise end of the positive electrode or the negative electrode is shifted inwards as compared with the lengthwise end of the positive electrode or the negative electrode. Therefore, the positive-electrode lead or the negative-electrode lead is not caught by the sealed portion of the case of the solid-electrolyte battery when the wound positive electrode and negative electrode are accommodated in the case of the solid-electrolyte battery.
Other objects, features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.